Insulation Displacement Termination (IDT) connectors allow mass termination of multiple wires in a multiple position connector product. By having terminals which cut through a wire jacket to make an electrical contact with the central solid conductor or group of strands in a wire, IDT connectors eliminate any required preparation of the wire end before the wire gets attached to the connector. IDT connectors in wire harnesses eliminate many wire assembly tasks such as insulation stripping, crimping to individual terminals or contacts, or soldering. IDT connectors are especially convenient for terminating wires which have been grouped in advance or manufactured as a unitary group, such as ribbon cable.
IDT connectors for typical cable harnesses are designed with an insulator housing holding one or more linear arrays of IDT terminals, and a backing plate or clip. The wires are lain en masse over their proper terminals and the backing plate (if included in the design) is positioned above the wires to form a sandwich. A press operation crushes the sandwich together and the backing plate forces the wires to become impaled upon the IDT terminals. The terminals pierce the wire insulator material, and encounter the central metal conductors. Common conductor materials include copper, aluminum, and brass and bronze alloys. Precious metals such as gold silver and platinum are also used but much more rarely. Thus most metal conductors received into wire harness cable end connectors will be non-precious metals which have accrued an external oxide film from contact with Earth atmosphere at some point in the wire manufacturing process.
For the best electrical interconnection, the oxide films on the wire strands and on the terminals must be displaced to expose fresh metal and to forge fresh metal to fresh metal contacts. This displacement may occur by scraping of the wire by the terminal during the crush process, or by deformation of the wire strands so that the oxide coating is stretched apart and fragmented to reveal fresh metal underneath. Yet even after a successful electrical interconnection is made, a minimum crushing force must be maintained over the life of the wire harness. Oxide films will grow on exposed fresh metal at the contact interface and may propagate over time to wedge apart previously bonded conductors, resulting in increased contact resistance, performance decay, loss of signal integrity, electrical noise, and intermittent interruption of electricity intended to pass through to the device to which the cable is attached.
Thus during and after assembly, sufficient pinching force must be developed and maintained by each IDT terminal to create and preserve “gas tight” metal to metal contact and durable and reliable electrical performance. Many previous designs fail to maintain good pinching force over a service lifetime, especially in applications where vibrations or thermal or mechanical shock cause individual conductive strands to drift from their originally installed positions.
Wire harnesses are also often used to electrically interconnect two pieces of equipment that move with respect to each other, or which are subject to mechanical shock or vibration, or temperature extremes or thermal shocks. In these and other application environments, IDT connectors must also resist a wire being pulled out of a terminal.
It is sometimes desired to supply an electrical device with high power to some of its subassemblies and low power to others. A common arrangement supplies a small number of larger, heavy-duty wires for motive power, solenoids, or heating, while a larger number of smaller, finer wires or ribbon cable is used for parallel data, digital signaling or digital control of the device. Some devices may require several intermediate sizes of wiring.
Conventional IDT designs allow only for connecting multiple wires of only one common wire gauge size, i.e, the same wire size, at a time. A common design for IDT contacts is the tuning-fork contact which has a pair of blades united at their base, so that an insulated wire inserted between the blades gets its insulation skived off (or pared off) on both sides. The gap between the two blades of the tuning fork forms a deep “V” which forces the conductive strands of a multiple strand wire together to form a plurality of gas-tight interconnections, However, a tuning fork contact of a given size can only successfully grab a narrow range of wire sizes, and if a wide range of wire sizes are to be connected through the same cable end housing, then such the insulator housing must be populated with a contacts of a number of different designs, each capable of handling its own narrow range of wire size, because if an oversize wire is inserted into the typical tuning fork or v-notch contact design, either the tuning fork deflects too much and loses its pinching force due to plastic deformation of its blades, or one or more strands of the inserted wire become cut clean off or shorn during the installation. The result is an unreliable electrical contact susceptible to long term degradation of electrical properties or excessive contact resistance due to an insufficient number of strands having made good electrical bonds with the contact.
The manufacturing of wire harness assemblies is a very labor intensive process is made even more complicated when for multiple wire sizes within a cable harness, each size must use its own dedicated cable end connectors. For example, the spring loaded contacts of U.S. Pat. No. 9,543,665 to Sabo require individual wires to be inserted into keyhole-shaped slots shown in FIG. 2A of that document. Most IDC contact designs use a vertical plate with a slot of a predetermined width, as seen in FIG. 1B and 1C of Sabo. Plates having a slot, or even an effectively serrated slot as in Sabo are best for connecting to solid wire. The initial compression afforded by a vertical plate and slot design deteriorates when multiple-strand wires are inserted. Vibration, tension, and other environmental conditions may allow the individual strands of wire to rearrange themselves over time, causing loss of contact force or pinching force onto these conductive elements, resulting in loss of electrical integrity of the connection.
In addition to being primarily suited only for solid wire connections, each slotted plate design can only handle a narrow range of wire size. Terminating multiple wire sizes into a single connector insulator housing usually requires a mix of contact styles each dedicated to one size or style of wire to be terminated. U.S. Pat. No. 5,890,924 to Endo et al, and U.S. Pat. No. 7,955,116 to Bishop have slotted vertical plate contacts that illustrate these limitations. Also, vertical plate and slot contacts cannot dynamically maintain contact normal force if the internal conductors of a multi-strand wire rearrange themselves in response to initially established pinch forces. This is also a limitation of terminals having two separate, substantially vertical and rigid plates receiving a wire inserted into a slot or gap between these features. An example of such a slot is seen between items 32 and 34 in FIG. 1 of U.S. Pat. No. 4,385,794 to Lucius. The bent plate features act the same as a vertical plate with a vertical slot.
Where several connections must be made at a particular site, the opportunity for error, mis-wiring, or damage increases with the number of attachments to be made. It would be an improvement in labor costs and design simplicity to be able to offer an IDT interconnection system which could handle mixed wire sizes in a single insulator housing of a cable end connector.
Lastly, cable end connector assembly may be simplified if all IDT terminals in a cable end receive their designated wires from a single direction, so that a simple press tool descending from above may be used to successfully and reliable install each wire into its designated terminal in a single operation.